Why does my 95 Mustang GT 5.0 engine idle rough?


Asked by Jun 05, 2012 at 09:15 PM about the 1995 Ford Mustang GT Coupe

Question type: Maintenance & Repair

I think my water pump is on it's way out. There is a noise from that area of the motor but I can't tell if
it's the water pump or the idler/tensioner pulley (on top). The engine idles rough and also stalls out.
Mileage has been getting progressively worse as the noise is getting louder. Could either one of these
cause the engine to stall and decrease fuel mileage? I know it's not the alternator because it is new
and not the source of the noise. Also the coolant temp gage moves up and down with the RPM's. Any
feedback would be greatly appreciated. Thanks.

14 Answers


If the bearing is bad on the water pump it will make noise, and leak. But since you said it was the front of the motor, and it stalls, I will say your fan clutch is shot. With the engine off, try to spin the fan blade by hand. A normal fan clutch will spin about a half to full rotation. I suspect you won't be able to move your. Make sure when you get a new one, you get a thermatic one.

2 out of 2 people think this is helpful.

ok sorry upon closer review it is not the water pump but looks to be the oil pump. there is no fan clutch as the rad has been replaced and an electric fan added. what ever it is has similar size hose going to the engine crank case area.....

1 out of 1 people think this is helpful.

if your oil pump makes noise I'd be tradin the car off !!


tune it up with a new cap and rotor,spark plugs and a good set of plug wires ..

3 out of 3 people think this is helpful.

Hmm, oil pump? I think maybe you mean the Harmonic Balancer? The rubber gasket inside tends to wear, adding drag to the motor? Do you notice a wobble at idle? http://www.ehow.com/how_8055804_replace-mustang-5-liter-engine.html


did you mean the power steering pump ?


I know it is not PS pump. and not harmonic balancer either. There is a pump of some sort at the bottom left - looking at the front of the motor. the noise may be normal but I can't be sure. The only other thing is that the coolant temp. gage moves with the pulsing idle........

2 out of 2 people think this is helpful.



I have a large manual to look at and the troubleshooting options are vast but I do think it has to do with coolant. it surprisingly was the first option to look at and I think it is valid. I have a high performance distributor cap, rotor, plugs and wires and not old enough to cause the idle issue -- in my opinion. it does seem electrical - perhaps one of the many censors. I work full time and dont have a lot of time to research this. I am just reading up on it and slowly eliminating possibilities..... for now..... thx Denis for weighing in...:)


never assume your cap is'nt cracked and if yo made the wires from a cut and fit set don't assume one end is'nt burned off either . all it takes is a bad crimp or a cut in the silicone jacket of a wire even under the boot . it'll miss like the dickens ... your high perf cap is all the more reason to check it ... ECHLIN from the napa store used to make the best caps ...

2 out of 2 people think this is helpful.

also check the reluctor air gap if it has one ... with a .008 brass feeler gauge .. if the dist shaft is wobbly then thats your problem .... PBN

2 out of 2 people think this is helpful.

well even the super genius has a brain fart now and then .... Smog pump , or as the technoids would say AIR injector pump.. this unit pumps air into the exhaust manifold after a certain speed is reached .. the additional air in the exhaust system fortifies the volcano reaction taking place in the catalitic converter which burns up leftover co2 , hydrocarbons ,Nox ,etc...

3 out of 3 people think this is helpful.

EUREKA!!!! Yes Peter that is exactly the unit. I followed the line off it and it leads to where the cat converters used to be. looks like bolts have been braised into the 2 openings it leads too. FYI I bought the car this way and have done none of the work to it. Now my question is -- can I by-pass that pump with a smaller serpentine belt.....one that is designed for the same motor minus the A/C??? And would this effect engine performance if it is possible to omit that pump all together??


If your cat. has been removed and the plumbing plugged , I can see no reason at all why you need to have the pump turning . I f you can find the right belt set up that will eliminate the smog pump I think you will be OK . just make double sure all the plumbing is plugged between the exhaust system and the smog pump or exhaust back pressure will burn out the check valve and blow thru the smog pump . PBN

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